mutable decl syntax change

examples/programs/bitwise/main.bro

@@ -18,7 +18,7 @@ c_count_shift func(value u8, count c_uint) u8 {
 c_count_fold u8 :: c_count_shift(3, 2)
 
 main func() i32 {
-	buffer Buffer = undefined
+	buffer Buffer := undefined
 	if (folded != 0) return 1
 	if (contextual != 255) return 28
 	if (contextual_shift != 128) return 29
@@ -50,7 +50,7 @@ main func() i32 {
 	if ((c_ushort(240) xor c_ushort(255)) != 15) return 26
 	if ((c_longlong(64) <<| 60) != maxval!(c_longlong)) return 27
 
-	value u8 = 3
+	value u8 := 3
 	value <<= 2
 	value |= 1
 	value xor= 5